When performing a joint replacement, it should be ensured that the reconstructed joint provides motion substantially the same as the original joint. For example, in a hip joint replacement, a portion of the hip and/or of the femur may be replaced with artificial components (the hip socket and/or femoral head may be replaced with an artificial parts). After the implant has been performed, the alignment and range of motion of the artificial joint should mimic that of the original joint.
In order to determine the relative position between the femur and the hip and, thus, quantify changes in the length of the femur after an implantation of the artificial components, it is known to directly attach a reference star to the pelvic bone and the femur (e.g., attaching the reference star directly to the respective parts using screw fasteners). Then by monitoring the movement of the reference stars as the joint is exercised through normal movement, the trajectory and range of motion can be ascertained and changes in length can be determined.